Cationic brush‐like terpolymer with pH responsive thickening behavior in a surfactant system

A new kind of cationic brush‐like terpolymer was synthesized by copper(I)‐mediated atom transfer radical polymerization (ATRP) of methyl ether poly(ethylene glycol) methacrylate (mPEGMA), poly(propylene glycol) methacrylate (PPGMA) and dimethylaminoethyl methacrylate (DMAEMA) in the presence of ethyl α‐bromoisobutyrate as ATRP initiator. The poly(PEG/PPG/DMAEMA) terpolymer was featured with a cationic backbone containing PDMAEMA segments and amphiphilic side chains composed of hydrophilic PEG and hydrophobic PPG short branches. The copolymer was characterized by ¹H NMR, Fourier transform IR and gel permeation chromatography. The thickening behavior of this copolymer in a surfactant system (sodium dodecyl sulfate, SDS) was extensively investigated by a rheological study. It was found that the copolymer can effectively thicken the SDS surfactant system at low concentrations of both copolymer and surfactant. More interestingly, the thickened SDS system by this copolymer showed dramatic pH responsive rheological behavior in the pH range 4–10. Thus the rheological behavior of the thickened SDS system was tunable by pH value. Based on our findings, a novel thickening mechanism is proposed for this kind of cationic brush‐like terpolymer. This kind of cationic brush‐like copolymer would be a new type of rheology modifier for advanced hair/skin care systems. © 2014 Society of Chemical Industry